A Java-implemented calculator applet

/**


@author Song Liang Peng


@version 2005.7.23


*/


import java.awt.*;


import java.awt.event.*;


public class Counter extends Frame implements ActionListener


{


TextField t=new TextField ("", 15);


Panel p1=new Panel ();


Panel p2=new Panel ();


button[] B=new button[10];


button Badd=new button ("+");


button Bsub=new button ("-");


button Bmul=new button ("*");


button Bdiv=new button ("/");


button Bpoint=new button (".");


button Bequal=new button ("=");


button Bsqrt=new button ("Open square");


button Bnull=new button ("Empty");


String str1= ""; STR1 and str2 store two input numbers


String str2= "";


String Operator=null; A symbol for storing subtraction and opening squares


Boolean first=true; Verify that the input is the first number


int countoper=0; Cumulative number of input symbols, even in addition to the operation will be used to


double result=0.0; Staging Results


double num1=0.0,num2=0.0; Two input numbers are converted to double storage when doing operations


Boolean error=false; Check whether the divisor is 0


//Construction method


public Counter ()


{


Super ("counter");


t.seteditable (FALSE);


for (int i=0;i<b.length;i++)


　{


b[i]=new Button (string.valueof (i));


P1.add (B[i]);


B[i].setactioncommand ("number");


B[i].addactionlistener (this);


　}


P1.add (Bpoint);


Bpoint.setactioncommand ("number");


P1.add (Badd); Number keys, symbol keys placed in the P1 of the panel


P1.add (bsub);


P1.add (Bmul);


P1.add (BDIV);


P1.add (bequal);


P2.add (BSQRT); The square and empty keys are placed in the P2 of the panel


P2.add (bnull);


Badd.setactioncommand ("Oper");


Bsub.setactioncommand ("oper");


Bmul.setactioncommand ("oper");


Bdiv.setactioncommand ("oper");


Badd.addactionlistener (this);


Bsub.addactionlistener (this);


Bmul.addactionlistener (this);


Bdiv.addactionlistener (this);


Bpoint.addactionlistener (this);


Bequal.addactionlistener (this);


Bsqrt.addactionlistener (this);


Bnull.addactionlistener (this);


p1.setlayout (New GridLayout (4,4,5,5));


p2.setlayout (New FlowLayout ());


Add (T, "North"); Frame's North Place input box, the panel is placed in center and South


Add (P1, "Center");


Add (P2, "South");


setlocation (400,200);


setSize (200,200);


SetBackground (color.red);


setvisible (TRUE);


Addwindowlistener (New Windowadapter () {//close window


public void windowclosing (WindowEvent e)


　 {


system.exit (0);


　 }


　});


}


//Implementation interface ActionListener


public void actionperformed (ActionEvent e)


{


button temp= (button) E.getsource ();


if (E.getactioncommand (). Equals ("number"))


　{


if (a)


　 {


Str1=str1+temp.getlabel ();


T.settext (STR1);


　 }


Else


　 {


Str2=str2+temp.getlabel ();


T.settext (STR2);


　 }


　}


Else if (E.getactioncommand (). Equals ("oper"))


　{


if (str1== "")///If no input is entered, click Operator to perform if,127 line of empathy


　 {


countoper=0;


first=true;


　 }


Else


　 {


countoper++;


if (countoper>1)


　　{


GetResult ();


　　}


Operator=temp.getlabel ();


First=false;


　 }


　}


Else if (E.getactioncommand (). Equals ("Open square")


　{


if (str1== "")


　 {


countoper=0;


first=true;


　 }


Else


　 {


countoper=1;


if (countoper>1)


　　{


GetResult ();


　　}


Double d=math.sqrt (double.parsedouble (str1));


str1=string.valueof (d);


T.settext (string.valueof (d));


First=false;


　 }


　}


Else if (E.getactioncommand (). Equals ("Empty")


　{


str1= "";


str2= "";


T.settext ("");


countoper=0;


first=true;


Error=false;


　}


Else if (E.getactioncommand (). Equals ("="))


　{


if ((str1== "") | |　 (str2== "")) Two numbers without losing all click on the equals sign to perform if


　 {


countoper=0;


first=true;


　 }


Else


　 {


GetResult ();


countoper=0;


　 }


　}


}


//Calculation results of the method


public void GetResult ()


{


num1=double.parsedouble (STR1);


num2=double.parsedouble (STR2);


if (operator.equals ("+"))


　{


result=num1+num2;


　}


Else if (operator.equals ("-"))


　{


result=num1-num2;


　}


Else if (operator.equals ("*"))


　{


result=num1*num2;


　}


Else if (operator.equals ("/"))


　{


if (num2==0.0)//Divisor 0 processing method


　 {


error=true;


　 }


Else


　 {


result=num1/num2;


　 }


　}


if (Error)


　{


t.settext ("error");


　}


Else


　{


T.settext (string.valueof (result));


str1=string.valueof (Result); After the operation of the results into the str1, str2 empty, in addition to the operation of continuous reduction to prepare


str2= "";


　}


}


//Main method


public static void Main (string[] args)


{


new Counter ();


}


}